Conventionally, pilots use weather radar to detect and avoid hazardous weather. Conventional radar systems may produce the desired results only in a limited environment. Typically, airborne threshold systems use thresholds for wet precipitation derived from ground-based weather radar thresholds generated from convective weather. Such thresholds have been set in accordance with reflectivity data which is applicable to typical convective weather systems in continental environments but not necessarily in maritime regions. It has been observed that maritime storm reflectivity differs substantially from continental storm reflectivity. Research by Zipser and Lutz in “The Vertical Profile of Radar Reflectivity of Convective Cells: A Strong Indicator of Storm Intensity and Lightning Probability?”, Monthly Weather Review of the American Meteorological Society, 1751-1759 (August 1994), characterizes the differences in reflectivity of continental versus maritime convective storms. Below the freezing altitude, the research shows that maritime storm reflectivity averages 8 dB below that of continental storms with peak maritime reflectivities observed at near sea level while peak continental reflectivities are observed at about the 8000 foot region. Above the freezing altitude, the reflectivity of maritime cells falls off at an average rate of 1.4 dB per 1000 feet versus the falloff rate of 0.45 dB per 1000 feet for continental storms. Peak reflectivity differences between the two populations of cells peak at about the 23 dB range at about 28,000 feet.
Conventionally, radar thresholds map radar return strength to a display with color representing rain rate or alternatively a weather threat assessment level. The threat level has been previously described as primarily a function of radar reflectivity and a weaker function of temperature, altitude, and latitude. However, because of the difference in maritime and continental weather, the conventional mapping while useful, does not completely allow successful operation of aircraft in maritime regions. The lower reflectivity of maritime weather does not allow for successful detection of significant convective weather systems during flight. Further, because of the ability of aircraft flying over maritime regions to circumnavigate storm systems, if recognized, it would therefore be desirable to provide an airborne radar system which has the ability to more accurately detect and report the existence and/or characteristics of maritime storms when operating in maritime environments and continental storms when operating in continental environments. It may be possible for a pilot operating radar manually to be able to compensate for the differences in maritime and continental weather as each pilot becomes familiar with the environment. However, knowledge by the pilot must be acquired, and further, an increase in pilot workload is also necessitated. Therefore, there is a need for an automated system of adjusting radar thresholds based on the presence of maritime or continental weather environments.
In addition, weather can vary within certain geographic regions. For example certain regions above the ocean and certain regions above land masses can have weather systems whose characteristics differ from other regions above the same ocean or land mass. Accordingly, it would be desirous to provide a radar system which can compensate radar detection in accordance with known characteristics of certain regions above oceans and land masses. In addition, weather characteristics can change according to seasonal and time-of-day variations. For example, certain radar reflectivities occurring during the monsoon season may indicate hazardous weather while those same radar reflectivities would indicate non-hazardous during another season. Similarly, weather radar returns at a certain time-of-day are more likely to indicate the presence of hazardous weather (e.g., afternoon) while those same returns are less likely to indicate the presence of a hazard at another time-of-day (e.g. early morning).
Still further the weather characteristics can vary by weather type. Often, the reflectivity of certain classes of weather systems may be lower than that which may be detected with the conventionally used on-board radar hardware. For example, stratiform weather has different characteristics than convective weather. Radar thresholds used for convective weather may not provide the appropriate warnings or rain rate indications if the weather is a different type, such as stratiform rain. In addition, weather associated with frontal systems has different characteristics than orographic systems.
Other hazard detection techniques are also affected by the type of weather that is in the environment. For example, models used to detect turbulence, hail, and lightning may not be as effective for one type of weather compared to another type of weather.
The maturity level of a weather cell can also affect weather radar sensing operations. A mature or decaying cell tends to be less hazardous than a cell that is growing. Radar returns and other parameters that indicate a hazard or rain rate for one maturity level may not accurately indicate a hazard for another maturity level.
Accordingly, there is a need for an automated system that adjusts radar tilt or threshold to improve detect ability of weather systems according to weather type, and/or weather maturity. There is also a need to adjust weather radar detection schemes based upon specific weather types and growth. There is further a need to adjust weather sensing in response to weather types by adjusting display thresholds, tilt angle, and/or system gain. Yet further, there is a need for a weather radar system that automatically adjust the weather sensing model in response to types of and/or weather.
It would be desirable to provide a system and/or method that provides one or more of these or other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the aforementioned needs.